LONDON (MarketWatch) -- BG Group on Tuesday said it's paying $1.3 billion to Exco Resources as the U.K. natural-gas producer teams up with the Dallas explorer to develop U.S. shale gas.

BG Group /quotes/comstock/23s!a:bg. (UK:BG.1,036, -1.00, -0.10%) said it will be getting a 50% interest in 120,000 net acres in East Texas and North Louisiana, much of what is in the "prolific" areas for the resource.

BG also is in talks to get a 50% interest in gas-gathering and transportation assets from Exco /quotes/comstock/13*!xco/quotes/nls/xco (XCO12.90, +1.78, +16.01%) .

Shale gas is natural gas stored in organic rich rocks that is difficult to produce.

The two firms say they will cooperate on further exploration and appraisal. The deal will add 2.6 trillion cubic feet of natural gas to BG's reserves. Exco estimates the current acreage potential has potential reserves between 4 and 6 trillion cubic feet.

"This alliance brings material new resources and supply to our existing U.S. business at a competitive price and in a prime location at the heart of the world's largest gas market," said BG CEO Frank Chapman.

"These domestic exploration and production activities yield strong synergies with the group's established LNG import and 3.5 billion standard cubic feet per day U.S. gas marketing business."